1. Field of the Invention
The present invention relates to a printer capable of recording on a sheet material having, on one side, a thermally activated adhesive surface which exhibits adhesive strength when heated, and on a sheet material having, on one side, an adhesive surface to which release paper is affixed.
2. Description of the Related Art
In recent years, many of sticker labels used for indication of a bar code, a price, and so on, are of a type having an adhesive layer on a backside of a recording surface (print surface) and stored in a state where a mount or release paper (liner) is affixed thereon for temporary adhesion. However, to use this type of sticker label (hereinafter referred to as an “ordinary label”) as a label, it is necessary to peel off the release paper from the adhesive layer, and accordingly, there is a disadvantage in that wastes inevitably occur.
In this connection, as a system which does not require the release paper, there have been developed a heat-sensitive adhesive label having, on a backside of a sheet base, a heat-sensitive adhesive layer which exhibits adhesiveness when heated while usually exhibiting non-adhesiveness, and a thermal activation device for heating the heat-sensitive adhesive layer on the backside of this label.
For example, as the above-mentioned thermal activation device, there have been proposed ones to which a variety of heating systems are applied, the heating systems using, as heating means, a heating roll, a hot air blower, an infrared radiator, an electric heater, a dielectric coil, and the like. Moreover, for example, in JP 11-79152 A (FIG. 1, paragraphs [0024] and [0025]), a technique has been disclosed, which includes bringing, into contact with the heat-sensitive adhesive label, a head having as heat sources a plurality of resistors (heater elements) provided on a ceramic substrate, such as a thermal head for use as a printing head of a thermal printer, thus heating the heat-sensitive adhesive layer.
Here, a conventional general configuration of a printer capable of recording on the heat-sensitive adhesive sheet will be described with reference to a thermal printer P2 of FIG. 10.
The thermal printer P2 of FIG. 10 is composed of a roll housing unit 20 which holds a tape-like heat-sensitive adhesive label 60 wound in a roll shape, a printing unit 30 which prints on the heat-sensitive adhesive label 60, a cutter unit 40 which cuts the heat-sensitive adhesive sheet 60 into labels with a predetermined length, and a thermal activation unit 50 as a thermal activation device which thermally activates a heat-sensitive adhesive layer of the heat-sensitive adhesive label 60. Note that “printing” referred to in this specification includes formation of images of a picture, a pattern, and the like besides those of characters and symbols.
The heat-sensitive adhesive label 60 has a structure in which, for example, a heat insulating layer and a heat-sensitive color-developing layer (printable layer) are formed on a front side of a sheet base, and the heat-sensitive adhesive layer obtained by coating and drying a heat-sensitive adhesive is formed on a backside thereof.
The printing unit 30 is composed of a thermal print head 32 having a plurality of heater elements 31 composed of relatively small resistors arranged in a width direction so as to enable dot printing, a printing platen roller 33 to be brought into press contact with the thermal print head 32 (heater elements 31), and the like. In FIG. 10, the printing platen roller 33 is rotated clockwise, and the heat-sensitive adhesive label 60 is transported to the right side.
The cutter unit 40 is one for cutting the heat-sensitive adhesive label 60 on which printing has been performed by the printing unit 30 into pieces with an appropriate length, and is composed of a movable blade 41 operated by a drive source (not shown) such as an electric motor, a stationary blade 42 opposed to this movable blade, and the like.
The thermal activation unit 50 is composed of a thermal-activation thermal head 52 serving as heating means having heater elements 51, a thermal activation platen roller 53 serving as transporting means for transporting the heat-sensitive adhesive label 60, draw-in rollers 54 which draw the heat-sensitive adhesive label 60 supplied from the printing unit 30 side into between the thermal-activation thermal head 52 (heater elements 51) and the thermal activation platen roller 53. In FIG. 10, the thermal activation platen roller 53 is rotated in a direction reverse to a rotation direction of the printing platen roller 33 (counterclockwise in the drawing) and transports the heat-sensitive adhesive label 60 to a predetermined direction (right side).
Note that, because a wrinkle becomes apt to occur in the heat-sensitive adhesive label or a transport failure becomes apt to occur when the label sags while being transported, generally, transport speed (print speed) by the above-described printing platen roller 33 and transport speed (activation speed) by the above-described thermal activation platen roller 53 are set equal to each other.
According to the thermal printer P2 thus configured, once the adhesiveness of the heat-sensitive adhesive label 60 is exhibited, sticking of an indicator label on a corrugated cardboard, a clear plastic wrap, a glass bottle, a plastic container, or the like, or sticking of a price or advertisement label can be directly performed. Accordingly, the thermal printer P2 has an advantage in that such release paper used for the ordinary label becomes unnecessary to make it possible to reduce cost. Moreover, the release paper turning to the wastes after usage is not required, and accordingly, the thermal printer P2 is desirable also from the viewpoints of resource savings and environmental protection.
Incidentally, in the printer P2 as shown in FIG. 10, when the cutting operation by the cutter unit 40 is performed, it has been necessary to stop the transport of the heat-sensitive adhesive label 60 for a period of time (for example, 0.4 sec) required for the movable blade 41 to move up and down. Specifically, the cutting by the cutter unit 40 is performed in a state where rotational drives of the printing platen roller 33, the draw-in rollers 54, and the thermal activation platen roller 53 are stopped.
For this reason, when a label length is longer than a distance from a cutting position of the cutter unit 40 to the heater elements 51 of the thermal-activation thermal head 52, the transport of the heat-sensitive adhesive label 60 is stopped in a state in which it is nipped between the thermal-activation thermal head 52 and the thermal activation platen roller 53.
As a result, the heat-sensitive adhesive layer that has started to exhibit its adhesiveness is undesirably stuck onto the thermal-activation thermal head 52 (heater elements 51), and the heat-sensitive adhesive label 60 is not smoothly transported even if the transport is resumed, causing malfunctions such as occurrence of so-called paper jam or transport failure. There is another problem in that heat from the heater elements 51 is transmitted to the printable layer (heat-sensitive color-developing layer) of the heat-sensitive adhesive label, thus developing this layer.
Accordingly, in the case of using the heat-sensitive adhesive label 60 with the above-described label length, it has been necessary to study a method (hereinafter, referred to as Method 1) enabling the cutting of the label without stopping the rotational drive of the thermal activation platen roller 53.
Besides this Method 1, it is conceivable to elongate the distance from the cutting position of the cutter unit 40 to the heater elements 51 of the thermal-activation thermal head 52 to be greater than the label length (hereinafter, referred to as Method 2). In this case, the above-described problems do not occur because the label length becomes shorter than the distance from the cutting position of the cutter unit 40 to the heater elements 51 of the thermal-activation thermal head 52. Hence, the cutting is performed after the rotational drive of the printing platen roller 33 is once stopped, the label is made to run again thereafter, and then the heat-sensitive adhesive layer of the label can be thermally activated.
However, in Method 2, it is necessary to secure the distance from the cutting position of the cutter unit 40 to the heater elements 51 of the thermal-activation thermal head 52 in accordance with the longest label length among a variety of lengths of labels to be printed. For this reason, a printer body is enlarged, and applications of the printer become limited. Hence, in order to make the printer capable of handling various types of labels without increasing a size of the printer or without regard to the label length, the above-described Method 1 must be adopted.
As a result of diligent studies, the inventors of the present invention found the following method as a method capable of performing the label cutting for labels having a length larger than the distance from the cutting position of the cutter unit 40 to the heater elements 51 of the thermal-activation thermal head 52 without increasing the size of the printer or without stopping the rotation of the thermal activation platen roller 53. In the found method, the transport speed (print speed) by the printing platen roller 33 is increased to be higher than the transport speed (activation speed) by the thermal activation platen roller 53, causing the label to sag within the distance from the cutting position of the cutter unit 40 to the heater elements 51 of the thermal-activation thermal head 52.
However, though this method is suitable in the case of the heat-sensitive adhesive label, two problems as will be described below are expected to occur when applying this method to an ordinary label (one in which a sheet label is stuck onto the release paper). Accordingly, this method is implemented only in a printer dedicated for the heat-sensitive adhesive label.    1) Ends of the sheet label on the release paper are peeled in a warped portion and caught on the entrance portion of the thermal activation unit 50, causing the paper jam.    2) The release paper is heated by the thermal-activation thermal head 52, causing danger in handling.